We propose an integrated, multidisciplinary program of basic and clinical research addressing challenges to the success of allogeneic HSCT used to treat of AML, ALL and MDS in older adults and patients lacking a histocompatible donor. The program's central theme of this program is: The exploration of novel approaches whereby injuries to normal host tissues induced by conditioning, infection and GVHD can be reduced or prevented, and resistance to pathogens and recurrent leukemia selectively enhanced. The program includes 6 research projects and 3 cores. Project 1 examines NK cell development, the role of KIR engagement of HLA ligand expressed by host and donor in modulating NK function, and, particularly, the contributions of activating KIRs, 2DS1 and 3Ds1 to resistance against leukemic relapse and CMV infections. Project 2 examines receptor ligand interactions governing monocyte response to stimuli from the microflora including their activation, mobilization and tissue distribution, and their capacity to both stimulate and participate in GVHD. Project 3 examines how T-cells when stimulated with allogeneic monocyte-derived dendritic cells in the presence of JAK-2 inhibitors induced into a durable state of anergy and the effects of JAK-2 inhibitors on responses are tumor antigens presented by other functionally distinct types of dendritic cells. Project 4 evaluates the regulation of IL-22, its role in the stimulation of enteri and thymic epithelial repair and its potential to reduce toxicities, modulate GVHD and enhance resistance to infection. Project 5 tests new monoclonal antibodies specific for WT1 peptide/HLA complexes, long-lived EBV T-cells transduced to express TCRs or chimeric antigen receptors specific for WT1/HLA complexes and new heteroclitic vaccines for adoptive immunotherapy of WT-1+ leukemias, Project 6 proposes 6 clinical trials testing new conditioning and both T-cell depleted and cord blood HSCT to reduce toxicities, potentiate hematopoietic and thymopoietic recovery and reduce TRM and new adoptive T-cell therapies for CMV infections or recurrent leukemia . The 3 cores include: Core A which provides all patient samples and evaluate grafts pre and post HSCT, Core B Biostatistics and Core C administrative support and oversight.